Radiation-shielding glasses providing safety against electrical discharge and being resistant to discoloration

ABSTRACT

Cerium-doped radiation-shielding glasses in the system of SiO 2  -PbO-alkali metal oxides, with a high absorption coefficient for high-energy X-ray and/or gamma- and, respectively, neutron radiation which are resistant to discoloration and exhibit a discharge stability of &gt;5×10 8  rad, consist essentially of (in % by weight) 
     
         ______________________________________                                    
 
    
     SiO 2             35-56                                                
Na 2  O                                                                
K 2  O            12-21                                                
Cs 2  O                                                                
PbO 2             24-46                                                
CeO 2             0.5-2.5                                              
CuO + Fe 2          0-0.05;                                            
______________________________________                                    
 
     for absorption of neutrons, the isotope Li 6  can furthermore be onctained therein, and SiO 2  can be substituted by B 2  O 3  and/or Gd 2  O 3  in an amount of up to 10% by weight and Gd 2  O 3  is present.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 07/341,996 filedApr. 24, 1989, now abandoned, which is a continuation-in-part ofapplication Ser. No. 07/342,670 filed Apr. 2, 1989, now abandoned, allincorporated by reference herein, which is a file wrappercontinuation-in-part of application Ser. No. 07/111,339 filed Oct. 22,1987 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to cerium-doped radiation-shielding glasses inthe SiO₂ -PbO-alkali metal oxide system, and especially to such glasseshaving a high absorption coefficient for high-energy X-ray and/or gammaradiation as well as neutron radiation. Radiation resistance againstdiscoloration is provided by the cerium oxide.

Radiation-shielding glasses are utilized in radiation-shielding windowsemployed in various facilities, e.g., research installations, employingor separating radioactive isotopes, and reprocessing plants. Thesewindows, made of different radiation-shielding glasses, must satisfycertain requirements:

(a) shielding of radiation from the hot cells with respect to theobserver in front of the window (biological protection) down to alegally determined minimal dose [mrem];

(b) maximally high transparency of the total window even with radiationexposure over a time period of several decades (radiation resistance);

(c) high stability of the glasses of the window against electricaldischarge (discharge stability).

As for (a):

Using Pb glasses with 24-75% by weight of PbO, it is possible toconstruct windows for any type of application by a combination ofvarious Pb glasses of different thicknesses so that biologicalprotection can be ensured in every instance.

As for (b):

The transparency of a window made of several glass panes of differentglasses depends on:

(1) transparency of individual panes,

(2) thickness of individual panes,

(3) light losses due to scattering on surfaces of the individual panes,

(4) number of panes affecting the interfaces in (3) ,

(5) radiation resistance of types of glasses used.

By selecting optically homogenous radiation-shielding glasses doped withCeO₂ against radiation discoloration, high transparency of a window canbe ensured even after operating a hot cell over several decades. Theradiation resistance of the glasses is customarily determined byirradiation tests with Co⁶⁰ at varying radiation doses. By reducing thenumber of individual panes and by surface refining of the panes by meansof leaching processes, cementing of several panes into a compound pane,and application of antireflection coats to glass surfaces, lightscattering losses on surfaces can be further reduced, and thetransparency of the window can be even more increased.

As for (c):

The presently utilized radiation-shielding glasses with contents of Pbbetween 24% and 75% by weight from the major manufacturers ofradiation-shielding glasses are safe from electrical discharge merely upto 5×10⁶ rad, i.e., after this dose of ionizing radiation, a discharge(electrical discharge) is observed in accordance with theinternationally conventional testing method of Eckels and Mingesz,described in the publications:

T. W. Eckels and D. P. Mingesz, Hot. Lab. Proceedings, Argonne Nat.Lab., 1970.

T. W. Eckels and D. P. Mingesz, Hot Lab. Proceedings, Argonne Nat. Lab.,Proceedings of 18th Conference of Remote.

This testing method is carried out as follows:

A falling pin of 725 g is dropped in a sliding tube from a height of 38mm onto a test cube (100 mm³) irradiated immediately beforehand (Co⁶⁰).If this causes, during this procedure

(a) a markedly visible blue flash and/or

(b) the quasi "frozen-in" flash in the glass, the so-called"Lichtenberg" figure, then the discharge limit is exceeded, and onespeaks of an electrical discharge.

Due to the discharge, the glass is destroyed and is unusable because ofthe then missing transparency.

The discharge limit, with data regarding the dose [rad] and testradiation [Co⁶⁰ ], such as, for example, 5×10⁶ [rad, Co⁶⁰ ], isdetermined starting with non-irradiated material, at constantlyincreasing doses and with interim discharge tests, and the material ischaracterized correspondingly.

Therefore, discharge resistance of 5×10⁶ rad means that, with Co⁶⁰irradiation below this dose, there cannot be initiation of electricaldischarge by the aforedescribed impact test. Spontaneous discharges,i.e., discharge phenomena without any external influence, such aspressure or impact, are obtained only at higher doses of radiation.

Radiation-shielding glasses free of Pb and having a relatively lowabsorption capability with respect to X-ray and/or gamma radiation haveadvantageously a discharge stability of >10¹⁰ (rad). For this reason,these glasses--cerium-stabilized borosilicate glasses being thenorm--are utilized in radiation-shielding windows of hot cells toprotect the Pb glasses against electrostatic discharge. In thisconnection, they serve, on the one hand, as a protective window againstpressure and impacts for the Pb-containing glasses arranged therebehind,and on the other hand as a moderator for the "hot" radiation. FIG. 1illustrates the structure, in principle.

The primary requirement to be met by radiation-shielding windows is themaximally complete absorption of radiation in the window by the glass,or the glasses. In this context, the shielding effect of theborosilicate glass with a volume proportion of about 1/4 is, however,less than 10% of the total absorption of the window. It can be seentherefrom how the design of the window is adversely affected by the"borosilicate glass" with respect to volume and weight of the window.

Conversely, U.S. Pat. No. 3,356,579 also discloses radiation-shieldingglasses utilized as "single-component" glasses, as well as windows madeof these glasses. These conventional, halogen-free glasses exhibitessentially the following composition (based on the batch in % byweight):

    ______________________________________                                                SiO.sub.2                                                                           41-50                                                                   PbO   30-36                                                                   CeO.sub.2                                                                           2.0-3.5                                                                 K.sub.2 O                                                                           16-21                                                           ______________________________________                                    

These glasses are highly resistant against discoloration and dischargeafter gamma irradiation up to at least 10⁸ Roentgen, but haveunsatisfactory neutron absorption properties. They exhibit densities ofbetween 3.1 and 3.5 g/cm³ and, with a thickness of 1 inch (=2.54 cm),have an initial transmission of above 90% at approximately 550 nm.

British Patent 764,575 discloses a gamma ray absorptive glass comprising17% to 25% K₂ O, 35% to 50% SiO₂, 26% to 45% P₅ O and 0.8% to 1.8% CaO₂.According to this reference lanthanides (didymiumoxid) should beavoided. There is no disclosure in the reference of the glasses having ahigh resistance to electric discharge or that such glasses would meetthe radiation qualities needed to avoid electric discharges in theglass.

In the prior art radiation-shielding glasses, compounds such as BaO andalso SrO are included because they are particularly absorptive of gammaradiation. Also, amounts of Na₂ O over 4 wt % are used because of theimproved fluxing qualities of the glass melt. Although other bivalentcompounds, e.g., MgO, CaO, ZnO and CdO are used in prior glasses, thesecompounds were not removed in purifying the glasses because it wasbelieved that these compounds could be tolerated. Also, glasses with aresistance to electrical discharge of greater than 5×10⁸ rad wereunknown and not producible from prior art glasses.

U.S. Pat. No. 4,520,115 discloses a glass composition for tube faces incathode ray tubes. It is known that such glasses can contain, e.g., PbOfor shielding properties against X-ray radiation, CeO₂ for a highresistance to discoloration and rare earths Gd to improve electronbrowning behavior. However, such glasses have only poorer transmissionqualities which do not matter in cathode ray tube faces which havethicknesses of only about up to 1 inch. The transmission qualities ofsuch glasses would in general be unsuitable in radiation shieldingwindows having greater thicknesses, for example, up to 1 meter, and inany case, over 30 mm.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide radiation-shieldingglasses absorbing gamma and X-ray radiation as well as neutronradiation, with a very high discharge resistance of >5×10⁸ rad uponexposure to high-energy radiation, and with a discoloration resistanceof much greater than 5×10⁸ rad (Co⁶⁰ radiation).

Another object is to provide windows made from such glasses.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

To attain the objects of this invention, there are providedradiation-shielding glasses absorbing gamma and X-ray radiation andneutron radiation with a resistance to electrical discharge of >5×10⁸rad with respect to high-energy radiation in the glass system(quantitative data in % by weight) of:

    ______________________________________                                        SiO.sub.2         35-56                                                       PbO               24-46                                                       Li.sub.2 O          0-2.5                                                     Na.sub.2 O        0-4                                                         K.sub.2 O          7-21        Σ = 12-21                                Cs.sub.2 O        0-5                                                         CeO.sub.2         0.5-2.5                                                      CuO                                                                                              0-0.05                                                    Fe.sub.2 O.sub.3                                                              ______________________________________                                    

and for the absorption of neutrons, SiO₂ is replaced in the glasses inan amount of up to 10% by weight by B₂ O₃ and/or Gd₂ O₃ and Gd₂ O₃ isalso present.

The K₂ O content is preferably equal to or greater than, on a percent byweight basis, 12.5, and preferably not less than 15.1, up to 21 and thesum of Na₂ O+K₂ O+Cs₂ O is preferably 15.1 to 21.

In addition to the above components, according to one embodiment of theinvention, the glass contains not more than 2.4% by weight of (Li⁶)₂ O.

Still further, the glasses can contain refining agents As₂ O₃ and/or Sb₂O₃, halogens F and/or Cl, and sulfates in quantities of up to 0.5% byweight.

According to another aspect of the invention, radiation-shieldingwindows are provided wherein at least a part of at least one pane ismade of the glasses of this invention.

Generally, there is incorporated into the glass about 2-10%, preferably3-8% of the sum of B₂ O₃ and Gd₂ O₃. In general, the glass contains,bearing these limitations in mind, 1-10% B₂ O₃ and/or 1-10% Gd₂ O₃, withthe preferred quantities being 2-7.00% B₂ O₃ and/or 2-7.50% Gd₂ O₃. In apreferred embodiment, the Gd₂ O₃ content is preferably at lest 10 ppm,more preferably from about 0.001 to 1.5 wt %, most preferably from about0.004 to 0.25 wt %.

The lower the amount of SiO₂ in the glass, the higher the amount of thesum of B₂ O₃ and Gd₂ O₃ which is required, but at least 35% SiO₂ must bepresent.

In a preferred embodiment, the total content of the Na₂ O, K₂ O and Cs₂O is from about 15.1 to 21 wt %. The glass is also free from MgO, CaO,SrO, BaO, ZnO, CdO, and preferably also free of Al₂ O₃. It is alsopreferred that the Na₂ O content is not more than 4 wt %.

It has surprisingly been found that the absence of MgO, CaO, SrO, BaO,ZnO and CdO and also preferably Al₂ O₃ leads to a radiation-shieldingglass having good transmission qualities and the highest knownresistance to electric discharge. It has been found that if only minimalamounts of such bivalent compounds are in the glasses, the preferredhigh resistance to electric discharge was not obtainable. It was furtherfound that BaO and SrO which are normally present in radiation-shieldingglasses reduce the transmission of the glasses to an unsuitable value.It was further found that even small amounts of Al₂ O₃ lead to tinystones in the glass because the solubility of Al₂ O₃ in the glass meltappears to be very poor. If small amounts of Al₂ O₃ are in the glassmelt, the melting temperature must be raised from 1,400° to about 1,550°to get a clear glass melt. However, such a high melting temperature isundesirable; consequently, the radiation-shielding glasses arepreferably free of Al₂ O₃. The glasses made according to the presentinvention are particularly suitable for radiation-shielding glassesneeded in thicknesses of from about 30 to 1,200 mm.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the preceding text and the following examples, all temperatures areset forth uncorrected in degrees Celsius and all parts and percentagesare by weight, unless otherwise indicated.

Exemplary compositions according to the invention (in % by weight) andseveral properties are compiled in Table 1.

The discharge resistance and radiation resistance of the glasses weretested at the nuclear research facility Julich (KFA) with the gammaspectrum of burnt burner elements, and in the nuclear research facilityKarlsruhe (KfK) with the gamma radiation emitted by the isotope Co⁶⁰.

It was surprising, in this connection, that with the addition of thecomponents responsible for neutron absorption, B₂ O₃ and/or Gd₂ O₃ and,respectively, (Li⁶)₂ O, the excellent properties of theradiation-shielding glass described in U.S. Pat. No. 3,356,579 remainpreserved. It is also possible to attain a discharge stability of >5×10⁸rad, whereas the gamma-ray-absorbing, conventional glasses are disclosedas being stable against electrical discharge to only about 1×10⁸ rad.

                                      TABLE 1                                     __________________________________________________________________________    1         2   3   4   5   6   7   8   9   10                                  __________________________________________________________________________    SiO.sub.2                                                                           53.80                                                                             44.85                                                                             49.20                                                                             48.60                                                                             47.20                                                                             36.70                                                                             42.00                                                                             36.65                                                                             42.30                                                                             43.90                               PbO   24.20                                                                             33.05                                                                             27.80                                                                             24.20                                                                             27.80                                                                             33.10                                                                             33.10                                                                             33.10                                                                             30.90                                                                             33.10                               Li.sub.2 O                                                                          --  0.30                                                                              0.30                                                                              --  0.30                                                                              0.50                                                                              0.30                                                                              --  0.30                                                                              0.30                                Na.sub.2 O                                                                          1.20                                                                              --  0.60                                                                              --  0.60                                                                              --  --  --  --  0.70                                K.sub.2 O                                                                           14.60                                                                             17.80                                                                             15.10                                                                             18.10                                                                             15.10                                                                             18.30                                                                             17.80                                                                             18.30                                                                             17.80                                                                             17.80                               Fe.sub.2 O.sub.3                                                                    --  --   0.001                                                                            --   0.001                                                                             0.001                                                                            --  0.05                                                                              --  --                                  As.sub.2 O.sub.3                                                                    --  --  0.15                                                                              --  0.15                                                                              0.30                                                                              --  0.30                                                                              --  --                                  F     --  0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                CeO.sub.2                                                                           1.80                                                                              1.80                                                                              1.40                                                                              1.40                                                                              1.40                                                                              0.90                                                                              1.60                                                                              1.40                                                                              1.50                                                                              1.00                                Gd.sub.2 O.sub.3                                                                    --  2.00                                                                              5.25                                                                              7.50                                                                              5.25                                                                              10.00                                                                             2.00                                                                              --  2.00                                                                              --                                  B.sub.2 O.sub.3                                                                     2.00                                                                              --  --  --  2.00                                                                              --  3.00                                                                              10.00                                                                             5.00                                                                              3.00                                (Li-6).sub.2 O                                                                      2.40                                                                              --  --  --  --  --  --  --  --  --                                  ρ[g/cm.sup.3 ]                                                                  3.04                                                                              3.33                                                                              3.21                                                                              3.12                                                                              3.22                                                                              3.52                                                                              3.34                                                                              3.35                                                                              3.24                                                                              3.28                                Tg [°C.]                                                                      543                                                                               512                                                                               554                                                                               562                                                                               541                                                                               535                                                                               509                                                                               501                                                                               514                                                                               508                                T 450 nm                                                                            71.5                                                                              65.3                                                                              67.1                                                                              68.5                                                                              64.8                                                                              63.2                                                                              66.4                                                                              69.8                                                                              66.5                                                                              69.6                                5 mm                                                                          T after                                                                             38.5                                                                              45.9                                                                              43.2                                                                              44.5                                                                              47.4                                                                              45.6                                                                              48.0                                                                              36.3                                                                              46.6                                                                              37.5                                5 × 10.sup.8 rad                                                        Discharge                                                                           no discharge up to 5 × 10.sup.8 rad                               __________________________________________________________________________

With the glasses of this invention, windows can be built that are lesscomplicated in their structure. It is possible to obtain a highertransmission by reducing the thickness of the windows while retainingthe permissible radiation threshold values on the cold side.

The radiation windows according to this invention may have multiplelayers of glass, e.g., 2 or more, preferably 2 to 8 layers, wherein atleast one layer is or comprises the glass according to this invention.

This will be demonstrated by way of example, using FIGS. 2a, b and 3a, band 4 and the subsequently disclosed Tables 2, 3 and 4. The windowsaccording to FIGS. 2a and 3a are made of commercially available glasses,whereas the glasses of this invention are used in the windows accordingto FIGS. 2b and 3b. In both examples, the two glasses having thedensities of δ=2.53 g/cm³ and δ=3.23 g/cm³ are substituted by a singleglass having a density of δ=3.23 g/cm³.

                  TABLE 2                                                         ______________________________________                                        Source:           Co.sup.60                                                   Activity:         10.sup.4 Ci                                                 Dose rate, "hot" side:                                                                          2.6 × 10.sup.5 rad/h                                  Maximally permissible                                                                           2.5 × 10.sup.-3 rad/h                                 dose rate, "cold" side:                                                       Wall:             concrete, density 3.5 g/cm.sup.3                            ______________________________________                                                         Window 2a Window 2b                                          ______________________________________                                        Discharge stability                                                                            >10.sup.6 >5 × 10.sup.8                                (rad)                                                                         Thickness (mm)   970       930                                                Transmission, 589 nm                                                                            52        56                                                (%)                                                                           Dose rate, "cold" side                                                                         2.1 × 10.sup.3                                                                    1.8 × 10.sup.-3                              (rad/h)                                                                       ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Source:          Cs.sup.137                                                   Activity:        10.sup.4 Ci                                                  Dose rate, "hot" side:                                                                         6.7 × 10.sup.5 rad/h                                   Maximally permissible                                                                          3.5 × 10.sup.-3 rad/h                                  dose rate, "cold" side:                                                       Wall:            Pb of a density of 11.4 g/cm.sup.3                           ______________________________________                                                         Window 3a Window 3b                                          ______________________________________                                        Discharge stability                                                                            >10.sup.6 >5 × 10.sup.8                                (rad)                                                                         Thickness (mm)   730       660                                                Transmission, 589 nm                                                                            60        64                                                (%)                                                                           Dose rate, "cold" side                                                                         1.3 × 10.sup.-3                                                                   1.3 × 10.sup.-3                              (rad/h)                                                                       ______________________________________                                    

These exemplary window constructions do not restrict the broad range ofusage of the glasses according to the composition range claimed.

The installation of the windows into Pb walls represents, with the useof the glasses according to this invention, a substantial simplificationin the structural design of the windows and of the window frames.

The roughly sketched structure of a Pb-wall window (FIG. 3) clarifiesthe complexity of the mounting or frame structure of the windowconstruction which seems to be of excessive dimensions with respect tothe Pb wall but is necessary for the shielding effect. Essentialadvantages for a simpler window design would already ensue in this casewith a saving of glass of >10 volume percent (see FIGS. 3a and 3b) byelimination of the Pb-free glass proportion and by using the glasses ofthis invention. On account of these matters, these windows not onlysatisfy the three primary requirements for radiation-shielding windows:

(a) biological protection,

(b) transparency, radiation resistance, and

(c) discharge stability,

but, with a substantially lesser use of glass, even improve thetransparency and the viewing angle of the window. The latter, with alarger field of view, results in improved monitoring of a "hot" cell.

FIG. 4 describes an embodiment of the invention wherein the radiationwindow comprises 6 layers A-F. At least one of the layers A-D comprisesthe glass according to this invention. The wall liner is preferablysteel built into a concrete wall, and the window frame is, e.g., caststeel or cast iron. Table 4 discusses the physical properties of theradiation shielding (RS) glasses, wherein the first number refers to thedensity, and the G number refers to the CeO₂ content.

                                      TABLE 4                                     __________________________________________________________________________    Physical Properties of RS                                                            Stabilized Glasses                Nonstabilized Glasses                Glasses RS                                                                           253-G18                                                                            253-G25                                                                            323-G15                                                                              323-G19                                                                            420-G07                                                                             S20-G05                                                                             253  360  520                        __________________________________________________________________________    Density                                                                              2.53 2.53 3.23   3.23 4.20  5.20  2.53 3.60 5.20                       (g/cm.sup.3)                                                                  CeO2-content                                                                         1.8  2.5  1.5    1.9  0.7   0.5   --   --   --                         (weight %)                                                                    PbO-content                                                                          --   --   34     33   58    71    --   45   71                         (weight %)                                                                    Radiation                                                                             10.sup.8 Gy                                                                       >10.sup.8 Gy                                                                       >5 × 10.sup.6 Gy                                                               10.sup.7 Gy                                                                        10.sup.6 Gy                                                                         5 × 10.sup.6 Gy                                                               10.sup.3 Gy                                                                        10.sup.3 Gy                                                                        10.sup.3 Gy                resistance                                                                    (Dose) for Ti                                                                 Radiation                                                                            >10.sup.8 Gy                                                                       >10.sup.8 Gy                                                                        5 × 10.sup.4 Gy                                                               10.sup.8 Gy                                                                        2 × 10.sup.4 Gy                                                               2 × 10.sup.4 Gy                                                               --   --   --                         resistance                                                                    (Dose) for                                                                    electrical                                                                    discharge                                                                     __________________________________________________________________________     1 Gy (Gray) = 100 rad                                                    

The approximate weight composition of some of the RS layers set forth inthe table are given below:

    ______________________________________                                        (a)     RS-253-G18     70%    SiO.sub.2                                                              10%    B.sub.2 O.sub.3                                                        9%     K.sub.2 O                                                              8%     Na.sub.2 O                                                             1%     BaO                                                                    2%     CeO.sub.2                                       (b)     RS-360 (F2)    45%    SiO.sub.2                                                              9%     K.sub.2 O + Na.sub.2 O                                                 45%    PbO                                             (c)     RS 520 (SF6)   27%    SiO.sub.2                                                              71%    PbO                                                                    2%     Na.sub.2 O + K.sub.2 O                          ______________________________________                                    

The areas of the glass layers can, if desired, telescopically decrease,with the layer at the radiation side having the greatest area.

The thickness of the layers B to E of the glass of the invention is atleast 20 mm to 1200 mm, preferably 150 to 500 mm, most preferably 200 to250 mm. The thickness of the total window (all layers) is about that ofthe wall or more. The area of layers A to F is at least about 100 mm×100mm to 1700 mm×1700 mm, preferably 600 mm×500 mm to about 1200 mm×1200mm. The ratio of the edges is about 1:1 to 1:2, preferably about 1:1.

The thickness of the concrete wall is, e.g., at least about 600 mm to1800 mm; the thickness of a Pb wall is at least about 100 mm to 400 mm.

The glasses in the figure have, e.g., the following composition, withthe proviso that at least one of layers A-D has the composition of theglass according to this invention.

Layer A: A glass according to this invention, or another stabilizedglass, e.g., RS 253--G 18 or RS 253--G 25;

Layer B: A glass according to this invention or another stabilizedglass, e.g., RS-253 G 18 or RS 253--G 25;

Layer C: A glass according to this invention or another stabilizedglass, e.g., RS 323 G 15;

Layer D: A glass according to this invention or another stabilizedglass, e.g., RS 323--G 15;

Layer E: A stabilized glass, e.g., RS 520--G 05, or a nonstabilizedglass, e.g., RS 323, RS 360, or RS 520;

Layer F: A stabilized glass, RS 323--G 19, or a nonstabilized glass,e.g., RS 253 or any other suitable glass or plastic glass.

Preferably, the glass layer A is easily exchangeably arranged becausethe high radiation causes high aging (electrical discharge) of the firstwindow. Also, the last layer (F) may be easily exchangeably arrangedbecause there might be mechanical damage. The layer F is a protectionlayer for layer E (e.g., RS 250), because the glasses used are lessresistant against chemical or mechanical attack. The thickness of layerA is at least about 15 mm to 50 mm, preferably about 20 mm. Thethickness of layer F is at least about 3 mm to 25 mm.

    ______________________________________                                        Practical Example for 10 kg of Glass                                          ______________________________________                                        Quartz powder          43,960 g                                               Minium, Pb.sub.3 O.sub.4                                                                             33,920 g                                               Lithium carbonate      750 g                                                  Potassium carbonate    25,880 g                                               Sodium carbonate       1,210 g                                                Potassium bifluoride   400 g                                                  Cerium(IV) oxide       1,005 g                                                Boric acid (H.sub.3 BO.sub.4)                                                                        5,310 g                                                ______________________________________                                    

The homogeneous mixture is melted in a quartz crucible or in acontinuously operating melting tank with quartz melting unit at between1,220° and 1,300° C. After a subsequent refining step of several hoursat temperatures of between 1,300° and 1,350° C., the melt is homogenizedwith a Pt stirrer. The bubble-free melt is then further homogenizedwithout schlieren with the stirrer while cooling to 1,250° C., pouredinto a mold at 1,180°-1,210° C., and uniformly tempered down to roomtemperature at about 530° C. in a cooling furnace.

In Table 5 below are listed a number of preferred glass compositions (in% by weight) which have been made according to the present invention.

                  TABLE 5                                                         ______________________________________                                               1    2          3        4                                             ______________________________________                                        SiO.sub.2                                                                              46.8   46.896      45.4988                                                                              52.4985                                    PbO      33.05  30.10      33.0   24.4                                        Li.sub.2 O                                                                              0.30  0.30       0.35   2.40                                        Na.sub.2 O                                                                             --     0.70       0.65   2.00                                        K.sub.2 O                                                                              17.80  17.60      18.50  16.50                                       F         0.20  0.20       --     0.30                                        CeO.sub.2                                                                               1.80  1.20       2.00   1.90                                        Gd.sub.2 O.sub.3                                                                        0.05   0.004      0.0012                                                                               0.0015                                     B.sub.2 O.sub.3                                                                        --     3.0        ----                                               ______________________________________                                    

The glass compositions of all the tables contain no mention of MgO, CaO,SrO, BaO, ZnO and CdO and all have a high resistance to electricaldischarge and suitable transmission properties.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexample.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. Radiation-shielding glasses absorbing gamma andX-ray radiation and neutron radiation with a resistance to electricaldischarge of >5×10⁸ rad with respect to high-energy radiation in theglass system (quantitative data in % by weight) of:

    ______________________________________                                        SiO.sub.2       35-56                                                         PbO             24-46                                                         Li.sub.2 O        0-2.5                                                       Na.sub.2 O      0-4                                                           K.sub.2 O       15.1-21           Σ = 15.1-21                           Cs.sub.2 O      0-5                                                           CeO.sub.2       0.5-2.5                                                        CuO                                                                                            0-0.05                                                      Fe.sub.2 O.sub.3                                                              ______________________________________                                    

and SiO₂ being replaced in the glasses in an amount of 2-10% by weightof the sum of B₂ O₃ and Gd₂ O₃, with the provisions that at least 35% ofSiO₂ is present in the glass, and Gd₂ O₃ is present in an amounteffective to contribute to said resistance.
 2. Glasses according toclaim 1, further comprising not more than 2.4% by weight of the isotopeLi⁶ in the form of (Li⁶)₂ O.
 3. Glasses according to claim 1, furthercomprising refining agents As₂ O₃ and/or Sb₂ O₃, halogens F and/or Cl,and sulfates in quantities of up to 0.5% by weight.
 4. Aradiation-shielding window structure wherein at least a part of at leastone pane comprises a glass according to claim
 1. 5. Aradiation-shielding window structure wherein at least a part of at leastone pane comprises a glass according to claim
 2. 6. Aradiation-shielding window structure wherein at least a part of at leastone pane comprises a glass according to claim
 3. 7. Glasses according toclaim 1, wherein the sum of B₂ O₃ and Gd₂ O₃ is 3-8%.
 8. Glassesaccording to claim 1, wherein B₂ O₃ is present in an amount of 1-10%. 9.Glasses according to claim 1, wherein Gd₂ O₃ is present in an amount of1-10%.
 10. Glasses according to claim 1, wherein B₂ O₃ is present in anamount of 2-7.00%.
 11. Glasses according to claim 1, wherein Gd₂ O₃ ispresent in an amount of 2-7.50%.
 12. Glasses according to claim 7,wherein B₂ O₃ is present in an amount of 2-7.00%.
 13. Glasses accordingto claim 7, wherein Gd₂ O₃ is present in an amount of 2-7.50%.
 14. Aradiation-shielding window structure, wherein at least a part of atleast one pane comprises a glass according to claim
 7. 15. Aradiation-shielding window structure, wherein at least a part of atleast one pane comprises a glass according to claim
 8. 16. Aradiation-shielding window structure, wherein at least a part of atleast one pane comprises a glass according to claim
 9. 17. Aradiation-shielding window structure, wherein at least a part of atleast one pane comprises a glass according to claim
 10. 18. Aradiation-shielding window structure, wherein at least a part of atleast one pane comprises a glass according to claim
 11. 19. A wallmountable radiation shielding window having a high absorptioncoefficient for high energy X-ray and gamma radiation with a resistanceto electrical discharge of greater than 5×10⁸ rad with respect tohigh-energy radiation comprising at least one pane wherein at least apart of the window comprises a glass containing, in percent by weight,of:

    ______________________________________                                        SiO.sub.2       35-56                                                         PbO             24-46                                                         Li.sub.2 O        0-2.5                                                       Na.sub.2 O      0-4                                                           K.sub.2 O        7-21          Σ = 12-21                                Cs.sub.2 O      0-5                                                           CeO.sub.2       0.5-2.5                                                       Gd.sub.2 O.sub.3               > 10 ppm                                       CuO + FeO.sub.3   0-0.05                                                      ______________________________________                                    

and a mounting for supporting the at least one pane in a wall.
 20. Aradiation shielding window of claim 19, comprising at least two layersof glass.
 21. A radiation shielding window of claim 20, comprising 2 to8 layers of glass.
 22. A radiation shielding window of claim 19, whereinthe area of the window is at least about 600 mm×500 mm to about 1200mm×1200 mm.
 23. A radiation shielding window of claim 19, wherein thethickness of at least one layer is at about 30 mm to 1200 mm.
 24. Aradiation shielding window according to claim 19, having furtherresistance to neutron radiation and for the absorption of neutrons, SiO₂is replaced in the glass in an amount of 2-10% by weight of the sum ofB₂ O₃ and Gd₂ O₃ with the proviso that at least 35% of SiO₂ is presentin the glass.
 25. A radiation shielding window of claim 24, comprisingat least two layers of glass.
 26. A radiation shielding window of claim24, comprising 2 to 8 layers of glass.
 27. A radiation shielding windowof claim 24, wherein the area of the window is at least about 600 mm×500mm to about 1200 mm×1200 mm.
 28. A radiation shielding window of claim24, wherein the thickness of at least one layer is at least about 30 mmto 1200 mm.
 29. Radiation-shielding glasses absorbing gamma and X-rayradiation and neutron radiation with a resistance to electricaldischarge of greater than 5×10⁸ rad with respect to high energyradiation in the glass system (quantitative data in % by weight) of:

    ______________________________________                                        SiO.sub.2       35-56                                                         PbO             24-46                                                         Li.sub.2 O        0-2.5                                                       Na.sub.2 O      0-4                                                           K.sub.2 O       15.1-21           Σ = 15.1-21                           Cs.sub.2 O      0-5                                                           CeO.sub.2       0.5-2.5                                                        CuO                                                                                            0-0.05                                                      Fe.sub.2 O.sub.3                                                              ______________________________________                                    

the glasses are free from MgO, CaO, SrO, BaO, ZnO, CdO, SiO₂ is replacedin the glasses in an amount of up to 10% by weight of the sum of B₂ O₃and Gd₂ O₃, with the provision that at least 35% of SiO₂ and at least 10ppm Gd₂ O₃ are present in the glass.
 30. Glasses according to claim 29,wherein Gd₂ O₃ is in the range from 0.001 to 1.5 wt %.
 31. Glassesaccording to claim 29, wherein Gd₂ O₃ is in the range from 0.004 to 0.25wt %.
 32. Glasses according to claim 29, wherein the glasses are freefrom Al₂ O₃.
 33. A wall mountable radiation shielding window having ahigh absorption coefficient for high energy X-ray and gamma radiationwith a resistance of electrical discharge greater than 5×10⁸ rad withrespect to high-energy radiation in the glass system comprising at leastone pane wherein at least a part of the window comprises a glasscontaining, in percent by weight, of:

    ______________________________________                                        SiO.sub.2         35-56                                                       PbO               24-46                                                       Li.sub.2 O          0-2.5                                                     Na.sub.2 O        0-4                                                         K.sub.2 O         15.1-21                                                     Cs.sub.2 O        0-5                                                         CeO.sub.2         0.5-2.5                                                     CuO + F.sub.2 O.sub.3                                                                             0-0.05                                                    Gd.sub.2 O.sub.3  0.001-1.5                                                   B.sub.2 O.sub.3    0-10                                                       SiO.sub.2 + B.sub.2 O.sub.3 + Gd.sub.2 O.sub.3                                                  35.001-56                                                   ______________________________________                                    

the glass being free of MgO, CaO, SrO, BaO, ZnO, CdO, with the sum ofNa₂ O, K₂ O and Cs₂ O being 12-21 percent by weight, and a mounting forsupporting the at least one pane in a wall.
 34. Radiation-shieldingwindow according to claim 33, wherein the glass is free of Al₂ O₃.